Bicycle MechanicsBroken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

There is very little difference between makes of tubes, and they may well come from the same factory. Heavier tubes will lose air more quickly, and ones that are made for thinner tires but used in fatter tires are more stretched in the tire, so will lose air quickly. One of my tires hardly looses any pressure from 100 psi over a day, but the other looses nearly 5 psi. I could leave them several days without pumping, but I pump them every day I ride, so I dont have to bother trying to remember if it was 3 or 4 days since I pumped them. This is no problem if you have a decent floor pump. Car tires keep their pressure, because the rubber is 10 times thicker and they are only 30 psi - you dont want tires that weight on your bike.

It sounds like you have a mtb or something similar that doesn't require high pressure like road bikes. MTB tubes generally will lose about 2 to 4 pounds of pressure a day depending on the thickness of the tube; whereas road tubes will lose about 5 to as much as 40 in a day, again depending on tube thickness. A 145gram thorn resistent tube will loss far less air then a ultra thin 65gram racing tube will in a day. Latex racing tubes (found mostly in road tubular tires) will lose almost 1/2 of their psi in 24 hours!

Andrew P may be on drugs because not all tubes are the same; nor do thicker, thus heavier tubes lose air quicker then thinner lighter ones-if one would only think about this for a whole second you will know the answer. I've seen cheap tubes where the consistency of the wall thickness varied from paper thin in spots to 6 to 8 sheets thick in other areas! While it's true that a lot of tubes are made from the same factory in Taiwan, but each company plastering their brand on the tube has different quality controls depending on brand recognition and cost and profit margins.

And car tires DO NOT keep their pressure either! They do keep it longer then bicycle tires because the tire is thicker (and it's the tire that holds the air not a tube in a car); but a car tire will typically lose about 1 to 3 pounds of air a month depending on weather, meaning if the weather is hot you will generally lose more.

Funny that Andrew P would say "Heavier tubes will lose air more quickly" then turn right around and say that "Car tires keep their pressure, because the rubber is 10 times thicker" yet according to his analogy it should lose air faster! but of course he did mention that car tires generally only carry 30psi, but that's only 15psi less then you put in your bike tires, and some car tires carry as much as 42psi yet they also don't lose air fast.

Now having said all that mumbo jumbo here is the practical side of it. I currently use 65grm ultralight racing tubes that I pump to about 100PSI, these tubes lose about 30 psi a day. Now this would make you think that by the end of the week the tire should be completely flat..BUT as the pressure decreases the loss also decreases thus at the end of a week I still have about 50 psi in the tubes if I don't maintain the pressure. My MTB tubes that I pump up to 60psi will only lose about 10psi during the first week and less in the succeeding weeks.

As far as putting on a layer of silicon on the outside of a tube...I've never heard this being done in over 30 years of riding so I have no clue what Sogood is talking about. But silicon is porous so I can only assume that you would still lose some pressure over time. But then you would also have to deal with the silicon mess inside your tire and whether or not silicon would have any long term adverse effects on either the tube or the tire casing. I do know that some of those fix a flat in a can for car tires contain silicon, but tire manufactures warranties are voided if you use those products (actually any canned fix a flat) in tires. while still under warranty.

I know your purists will take exception, but when I have a slow leak or even a total flat, I put a pressurized can of tire sealer in my road tire. It does the trick, and doesn't foul the valve. The sealant stays in the tube and helps prevent future flats. My LBS has cans of this stuff that will fit a Presta or a Schrader. A can costs about $9, but it's worth it if you don't have to change a tire 20 miles from home. The pressure can inflates the tube to around 80 pounds.

__________________
"I am a true laborer. I earn that I eat, get that I wear, owe no man hate, envy no man's happiness, glad of other men's good, content with my harm." As You Like It, Act 3, Scene 2. Shakespeare.
"Deep down, I'm pretty superficial." Ava Gardner.

I know your purists will take exception, but when I have a slow leak or even a total flat, I put a pressurized can of tire sealer in my road tire. It does the trick, and doesn't foul the valve. The sealant stays in the tube and helps prevent future flats. My LBS has cans of this stuff that will fit a Presta or a Schrader. A can costs about $9, but it's worth it if you don't have to change a tire 20 miles from home. The pressure can inflates the tube to around 80 pounds.

It's not that we're purists, but rather the stuff doesn't work in pressures exceeding about 65psi, which means it works good in MTB tires but not in road tires. PLUS it adds weight to the tire, PLUS you have to haul that damm can around. BUT I haven't seen or tried that particular stuff your talking about: I went down to an LBS today and asked about it but they haven't heard of it either other then the stuff use in car tires you buy at auto stores, and that stuff will void a tire manufactures warranty.

Those fix-a-flat cures are best use as a limp home repair on MTBs, hybrids, comfort, and crusier bikes. My wife used a can. It did the job it was intended to do, but I changed the tube as soon as I had the time. (3 speed rear hub)

I used to use all that tire goo; Fix-a-flat, that green snot looking stuff - all kinds of stuff.

After plenty of experience, I gave it all up and just went to either fixing the leak or replacing the tube.

That tire goo has several dissadvantages:

1) Adds weight to the tire which is the worst place of all to add weight.
2) Doesn't always work.
3) Makes it difficult or impossible to fix punctures with a traditional patch.
4) Tire goo freezes in winter.

If you have a slow leak, remove the tube from the wheel and overinflate it until you find the hole. put a tooth;pick in the hole so you know where the hole is and repair with a patch kit.

1. Tubes lose air. Expect to loose at least a couple of pounds per day. If you are loosing much more, then yes, you prolly have a slow leak - replace the tube and repair the old one to use as a spare, as Mike instructed.

2. Because tubes loose air, you should check your tire pressure and pump as necessary before every ride.

3. Always carry a spare tube and/or patch kit, tire levers and a source of air, whether it be a pump or C02 cartridge.

__________________"Let us hope our weapons are never needed --but do not forget what the common people knew when they demanded the Bill of Rights: An armed citizenry is the first defense, the best defense, and the final defense against tyranny. If guns are outlawed, only the government will have guns. Only the police, the secret police, the military, the hired servants of our rulers. Only the government -- and a few outlaws. I intend to be among the outlaws" - Edward Abbey

1. Tubes lose air. Expect to loose at least a couple of pounds per day. If you are loosing much more, then yes, you prolly have a slow leak - replace the tube and repair the old one to use as a spare, as Mike instructed.

2. Because tubes loose air, you should check your tire pressure and pump as necessary before every ride.

3. Always carry a spare tube and/or patch kit, tire levers and a source of air, whether it be a pump or C02 cartridge.

Chipcom is obviously correct that bike tires lose air. Why is that? Where does it go? Does it sneak out of the valve or somehow get through the tube?

Why is it that I only have to check my automobile tires once in awhile, but my bike tires lose air frequently.

Chipcom is obviously correct that bike tires lose air. Why is that? Where does it go? Does it sneak out of the valve or somehow get through the tube?

Why is it that I only have to check my automobile tires once in awhile, but my bike tires lose air frequently.

Tubes, whether latex or butyl is porous similar to balloons which you have seen loose air in just a few days. Latex is the more porous then Butyl and that's why those you have to fill each day. Car tires are thicker but still loose air due to still being porous but takes far longer then a bike tire with their thin tubes. Though if you could fill your car tires with Nitrogen like some race cars do, you would loose air slower then with regular air because the molecules of nitrogen are larger then regular air which consist of Nitrogen and Oxygen, thus the larger molecules have a harder time trying to escape porous substances. Also because the molecules are larger with Nitrogen your tires run cooler which is the main reason some race cars use nitrogen.

Tubes, whether latex or butyl is porous similar to balloons which you have seen loose air in just a few days. Latex is the more porous then Butyl and that's why those you have to fill each day. Car tires are thicker but still loose air due to still being porous but takes far longer then a bike tire with their thin tubes.

More porous material + higher pressure per square inch.

__________________"Let us hope our weapons are never needed --but do not forget what the common people knew when they demanded the Bill of Rights: An armed citizenry is the first defense, the best defense, and the final defense against tyranny. If guns are outlawed, only the government will have guns. Only the police, the secret police, the military, the hired servants of our rulers. Only the government -- and a few outlaws. I intend to be among the outlaws" - Edward Abbey